I've sailed both sails on many days in the same size. 4.0, 4.4 and also 4.8 A friend has the 21 Pro and I have the 21 std version. We often switch the gear on the water to test, compare and fine tune a lot of things. We both came to the end that the difference is marginal on the water. The Pro has a slightly different feeling in the power build up. The lighter pro version helps a bit when u have to walk 1km+ to your spot but this is also a question of your mindset.

Difficult to answer your question in terms of durability. Depends highly on the skills of the sailor and your aimed wave spot. Since 2013 I've just killed one S1 in wave sailing conditions and this was my own fault. If you sailing a reef spot quite often I would maybe not take on of the lightest and most expensive sails on the market.